Fluorinated elastomers are known materials and include elastomers such as fluorocarbon elastomers, fluorinated thermoplastic elastomers, fluorosilicone elastomers, and phosphonitrilic fluoroelastomers. See for example, West, A. C. and Holcomb, A. G., "Fluorinated Elastomers", Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 8, pp. 500-515, 3rd ed., John Wiley & Sons, 1979 and also U.S. Pat. No. 4,158,678 (Tatemoto et al.), incorporated herein by reference.
Fluorinated elastomers are thermally stable and exhibit chemical- and solvent-resistance. Such elastomers have many valuable industrial uses, such as O-rings, seals, gaskets, hoses, etc. However, the elastomers are costly, and the route to finished rubber products can be complex, often requiring preliminary mixing of fillers, curatives and other adjuvants with the elastomer gum. Also, additional shaping of certain articles, e.g., hoses, is required prior to vulcanization. The cure process can generate considerable quantities of non-reusable scrap and, in addition, cured articles cannot be reprocessed, e.g., by injection molding or extrusion.
In contrast, engineering thermoplastics such as nylons, acetals, polyesters, polyphenylenes, and polycarbonates, and specialty thermoplastics such as polysulfones, aromatic polyesters and polyamide imides are readily processable and reprocessable, e.g., by injection molding or extrusion. They show a good balance of high tensile properties, compressive and shear strength, impact resistance, and retain their properties over a wide range of environmental conditions. However, these materials do not have elastomeric properties. See, for example, "Engineering Plastics", Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 9, p. 118 ff, 3rd ed., John Wiley & Sons, 1979.
Thermoplastic elastomers are known materials possessing both elastomeric and thermoplastic characteristics. These materials are becoming increasingly popular in industrial applications because of their ease of fabrication and general good physical properties. Thermoplastic elastomers are of two main types, (1) block and graft copolymers containing elastomeric and plastic polymer chain segments, and (2) blends of certain elastomers and thermoplastics. Examples of the latter class include blends of hydrocarbon elastomer and thermoplastic polymer such as blends of ethylene/propylene rubber (EPDM) with polyolefin thermoplastics, such as polypropylene or polyethylene. See for example, Coran, A. Y. and Patel, R., "Rubber-Thermoplastic Compositions., Part I," Rubber Chemistry and Technology, Vol. 53, p. 141 ff, Rubber Division, American Chemical Society, 1980; and also U.S. Pat. No. 4,130,535 (Coran et al.). The elastomer blend component is often crosslinked to promote elasticity and improve the properties of the thermoplastic elastomer, such as reduced permanent set, improved ultimate mechanical strength, improved fatigue resistance, greater resistance to attack by fluids, improved high-temperature utility, etc. They can also be rapidly fabricated into finished parts using thermoplastic processing equipment, and vulcanization during fabrication into finished parts is not required. See, for example, Coran, A. Y., "Thermoplastic Elastomers Based on Elastomer-Thermoplastic Blends Dynamically Vulcanized", Thermoplastic Elastomers: A Comprehensive Review, Chapter 7, p. 133 ff, Edited by Legge, N. R., et al., Hanser Publishers, 1987.
Although the thermoplastic elastomers described above have many desirable properties, there is a need for thermoplastic elastomers with increased high temperature performance and improved fluid resistance (e.g., oil and alcohol resistance) that are easy to process (e.g., by extrusion or injection molding).
European Patent Application No. 432 911 A1, published Jun. 19, 1991 describes certain fluorine-containing compositions comprising 50 to about 90 weight percent of crosslinkable fluorinated elastomer and 10 to about 50 weight percent of essentially fluorine-free thermoplastic polymer having a melt temperature or glass transition temperature greater than about 150.degree. C. The fluorinated elastomer may be present in the composition in a separate phase in a cured or partially cured form. One disadvantage of some of these compositions is that their viscosities are sufficiently high that they are difficult to extrude or injection mold.
Japanese Patent Application No. JP63-81159 (Ono et al.) discloses a thermoplastic elastomeric composition comprised of (A) 99-1 wt. % polyetherester amide (a thermoplastic elastomer), and (B) 1-99 wt. % rubber components selected from acrylic rubber, conjugated diene-vinyl cyan rubber and hydro-rubber, and fluoro rubber. The fluoro rubber includes copolymers of vinylidene fluoride and hexafluoropropylene. Although the application states that the thermoplastic elastomeric composition can be cured, it does not describe compositions containing a cured fluoro rubber phase dispersed in a continuous thermoplastic polymer phase.
Thermoplastic elastomers having good chemical resistance, thermal stability and processability are desirable, yet such materials have not been readily available. Thus, it would be useful to develop a thermoplastic elastomeric composition possessing all such properties.